In this paper, a steady 3D numerical study has been conducted on a 90 mm counter rotating lift fan to investigate its aerodynamic performance. The effect of axial distance between the fans and rotor speed are studied. A low thrust generation has been revealed from the simulation results due to the unfavourable working condition for the upstream rotor. Subsequently, an inlet guide vane (IGV) is geometrically designed to cause a preswirl effect at the inlet. Results show that the pressure ratio and total thrust are significantly improved at 10% by the IGV with a little sacrificing in efficiency. Such work can be a guidance in the further design and optimization.